1. Field of the Invention
The invention relates to a method of operating a gas turbine with a plurality of hybrid burners in a combustion chamber. The invention also relates to a gas turbine with a plurality of hybrid burners disposed within the combustion chamber. The principle of a hybrid burner is described in the article titled xe2x80x9cProgress in NOx and CO Emission Reduction of Gas Turbinesxe2x80x9d, by H. Maghon, P. Behrenbrink, W. Termuehlen and G. Gartner, ASME/IEEE Power Generation Conference, Boston, October 1990. Published, Non-Prosecuted German Patent Application DE 196 37 725 A1 describes a method and a device for burning fuel with air in a combustion chamber. The air is supplied to the combustion chamber through at least one air inlet and the fuel is supplied through to a plurality of burners. In this configuration, each burner has a characteristic phase response, for example an associated delay period, corresponding to a time duration after which an acoustic pulse in the combustion chamber causes a thermal pulse due to combustion of the fuel supplied to the burner. The supply of the fuel to the burners is controlled in such a way that the delay periods of the burners are essentially different from one another. The delay period of a burner corresponds to a phase difference at the location of the burner between an acoustic oscillation in the combustion chamber and a thermal oscillation at the burner. Such combustion oscillations are caused by the interaction between the acoustics of the combustion chamber and a release of thermal output during the combustion. These combustion oscillations can lead to high levels of noise annoyance or even to mechanical damage. In a configuration with a plurality of burners in a combustion chamber, the combustion oscillations emerging from the individual burners can reinforce one another. Because the burners are supplied with different fuel quantities, the delay periods for the burners are different. The delay period of a burner in a combustion chamber is composed of different summands, which can be respectively attributed to individual components of the system containing burners, the combustion chamber and the flame. The summands that can be related to the burner and the combustion chamber are mainly determined by the geometry of the burner and the combustion chamber. A summand that can be attributed to the flame itself is essentially determined by the properties of the combustion itself. The summand itself can be further broken down into a convective delay period, which characterizes a transport time for the transport of the reaction partners to the flame front where the combustion is initiated, a heating time, which gives the time for the heating of the reaction partners to the temperature necessary for ignition, and a reaction kinetics delay period which is determined by the course of the combustion itself. As a rule, the convective delay period clearly outweighs the two other summands. Different delay periods for the various burners lead to the fact that the combustion oscillations emerging from the individual burners can no longer reinforce one another.
It is accordingly an object of the invention to provide a method of operating a gas turbine and a corresponding gas turbine which overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, in which combustion oscillations are substantially suppressed. A further object of the invention is to provide a gas turbine that has favorable properties, in particular with respect to a low tendency to develop combustion oscillations.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of operating a turbine. The method includes the step of providing a gas turbine having a plurality of hybrid burners disposed in a combustion chamber. Each of the hybrid burners have a pilot burner and a main burner, and a pilot fuel quantity is supplied to the pilot burner. At least two of the pilot burners are operated with different pilot fuel quantities, a difference in the pilot fuel quantity being set in dependence on a load of the gas turbine.
According to the invention, the object directed toward the method is achieved by a method of operating a combustion configuration with a plurality of hybrid burners in a combustion chamber. Each of the hybrid burners has the pilot burner and the main burner and a pilot fuel quantity is supplied to each pilot burner. At least two of the pilot burners are operated with a different pilot fuel quantity, the difference in the pilot fuel quantity being set as a function of an effective output of the combustion configuration.
The pilot burner preferably operates as a diffusion burner, i.e. fuel and combustion air are mixed and burnt by diffusion in the combustion chamber. The main burner is a premixing burner, i.e. the fuel and the combustion air are mixed before entry into the combustion chamber and are subsequently burnt. In this configuration, the fuel mixture of the main burner usually ignites on the flame of the pilot burner.
The burner configuration effects the output. The effective output can, for example, be the output for a heating boiler or an output for driving a turbine. High effective outputs are achieved by the operation of the main burner, the pilot burners being mainly responsible for stabilizing the combustion of the main burner. At low effective outputs, the pilot burners can also operate exclusively as diffusion burners.
As described above, a combustion oscillation can develop in such a burner configuration. The invention is based on the knowledge that a static supply of a different fuel quantity to the burners in order to suppress combustion oscillations is not feasible over the whole range of the possible effective output, also referred to as the load, of the burner configuration. At lower effective outputs, the pilot burners must usually be supplied with a high quantity of fuel in order to provide stable ignition of a weak fuel mixture in the main burner. If now, in the case of at least two of the pilot burners, the respectively supplied pilot fuel quantities are set as a function of the effective output of the burner configuration, detuning of the burners relative to one another and adapted to the respective operating conditions, occurs. The supply of different pilot fuel quantities is matched to the minimum pilot fuel quantity required to stabilize the combustion. The burner configuration can, therefore, be operated stably at low loads, and, combustion oscillations can be effectively suppressed by the supply of different pilot fuel quantities to at least two of the pilot burners due to the different delay periods of the pilot burners brought about in this way.
The difference in the pilot fuel quantity preferably increases with increasing effective output (load). Therefore, it is possible to set a larger difference in the pilot fuel quantity at increased effective output without impairing the stability of the combustion. Since it is precisely at higher effective outputs that troublesome combustion oscillations occur, operation of the pilot burners with different pilot fuel quantity is particularly advantageous in this case for suppressing combustion oscillations.
At maximum load of the gas turbine, a major proportion of the hybrid burners are preferably operated with between one and two percent of a maximum pilot fuel quantity and the rest of the hybrid burners are operated with between 5 and 15 percent of the maximum pilot fuel quantity.
At effective outputs or loads above XX% (i.e. 60%) of the maximum effective output of the combustion configuration, a first number of the hybrid burners is preferably operated with a first pilot fuel quantity and a second number of the hybrid burners is preferably operated with a second pilot fuel quantity. The first number being more than XX (i.e. four) times as large as the second number and the second pilot fuel quantity being more than XX (i.e. two) times as large as the first pilot fuel quantity. At effective outputs above 60% of the maximum effective output of the burner configuration, it is sufficient to operate a comparatively small number of the hybrid burners with a pilot fuel quantity that is smaller than that of the other hybrid burners. In this way, an output release from the pilot burners is scarcely reduced and, nevertheless, combustion oscillation is effectively suppressed. The method is preferably employed in a gas turbine with an annular combustion chamber. This can be a stationary gas turbine or an aircraft engine. In the case of the large effective outputs of a gas turbine, very strong combustion oscillations can occur. It is precisely in the case of an annular combustion chamber that such combustion oscillations are practically impossible to predict and must be countered by additional measures. The different setting, as a function of load, of the pilot fuel quantities offers a simple and efficient method of suppressing combustion oscillations in this case.
According to the invention, the object directed toward a gas turbine is achieved by a gas turbine with a plurality of hybrid burners in a combustion chamber. Each of the hybrid burners has a pilot burner and a main burner. It being possible to feed a pilot fuel quantity to each of the pilot burners. A control unit is provided for the control, as a function of a load, of a supply of different pilot fuel quantities to at least two of the pilot burners.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of operating a gas turbine and a corresponding gas turbine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.